My old tap-and-die set (which I've now given to my son) had an adapter that would fit into a hex
die stock, with four square holes machined into it for driving taps. This is lacking in the newer
and larger set that I bought to replace the other one -- and appears, so far, to be available
*only* in sets. Anyone know where I can buy just that part?

A similar part can be seen here, at the far left just below the tap wrench:
http://www.sears.com/craftsman-37-pc...p-00952343000P